In the ever expanding area of computer communications systems the use of networking communications systems is becoming more and more pervasive. Problems have arisen in the amount of time it takes to transmit substantial amounts of information over slow systems (e.g. wireless and wired modems). A typical office environment utilizes a LAN of some type for telecommunications. A typical Ethernet runs at 10,000 kbps (thousand bits per second) while a token ring is capable of running at 16,000 kbps. The typical telephone line is capable of transmitting 56 kbps and usually transmits 28.8 kbps while the typical packet radio link is only capable of transmitting up to 19.2 kbps and averages 4.8 kbps. This is a significant reduction in response time from what one is used to experiencing on their workstation attached via LAN in the typical office to what one would see at their home or working remotely. This causes an unacceptable reduction in the responsiveness of a computer when the connection is changed from a fast connection to a slow connection.
The increase in the use of the Internet (or the World Wide Web) has drawn attention to this shortcoming. The Internet paradigm is one of clients (usually browsers) communicating with Internet servers. This communication in the web environment is also expected to be 'real-time' rather than the old telecommunications paradigm of e-mail or typical batch-type processing The communication between these clients and servers is machine independent and utilizes a connectionless, best-effort protocol. Each transaction between the client and the server is self-contained or "stateless" as it is currently termed. This increases the portability of the applications but also increases the amount of information which must be transferred between the client and the server to complete a given transaction. In addition, most web pages today contain graphics which are very large. While most browsers allow a user to execute in 'text only' mode, a majority of the users ignore this option due to the enhanced benefit that the graphics provide.
The growth of Java applets and the requirement to download complex applets (very large, approximately 10s of thousands of bytes) with associated JAR files (also very large, many over 100s of thousands of bytes) has also made transmission times unacceptable to many users, especially at network speeds of less than 56 kbps. JAR files are containers that hold multiple files which are collected into one large file for transmission. This container can be transmitted in either a compressed or an uncompressed form. This problem of repeated transmission becomes particularly burdensome when files must be repeatedly downloaded from one session to the next either because of a minor update to one of the objects in the container or because the browser does not retain cached objects across sessions.
Many software manufacturers make non-applet software available on the world wide web (the Web) in the form of ZIP or self-extracting ZIP archive files. ZIP archive files are container files that have a publicly known architecture. JAR files are actually a subset of the overall ZIP file architecture. The ZIP files can be downloaded directly with a Web browser, but such downloads take a significant amount of time. Some companies have created products that will compare a file with a previous version of the file prior to refreshing the file on the remote computer in an effort to reduce the response time as perceived by the user. An example of such a product is Novadigm's EDM. EDM compares a file to be transmitted to a remote computer with the copy of the file that was most recently sent to the same remote computer. If the file has changed it is resent; if it has not changed it is not resent. This is acceptable for most files but if the user had a previously downloaded version of the archive, it would be valuable to be able to download only the portions of the archive which had changed in order to bring the user to the current version of the product and not be required to retransmit the entire compilation. This would significantly reduce the transmission time for software distributors who were attempting to ship updates and fixes over the Web.